The Diamond Throne by David Eddings

In an ancient kingdom, the legacy of one royal family hangs in the balance, and the fate of a queen—and her empire—lies on the shoulders of one knight.Sparhawk, Knight and Queen’s Champion, has returned to Elenia after ten years of exile, only to find young Queen Ehlana trapped in a crystalline cocoon. The enchantments of the sorceress Sephrenia have kept the queen alive–but the spell is fading. In the meantime, Elenia is ruled by a prince regent, the puppet of the tyrannical Annias, who vows to seize power over all the land.Now Sparhawk must find the legendary Bhelliom, a sapphire that holds the key to Ehlana’s cure. Sparhawk and his companions will face monstrous foes and evil creatures on their journey, but even greater dangers lie in wait: for dark legions will stop at nothing to reach the radiant stone, which may possess powers too deadly for any mortal to bear.